Patients with inflammatory bowel disease often experience increased sensory responsiveness in the urinary bladder reflecting neurogenic bladder overactivity. This visceral symptom overlap involves neuronal cross-activation in the dorsal root ganglia (DRG) where the bladder afferent neurons are sensitized. The long- term goal of this project has been to understand the complex neuronal interaction between colonic and bladder sensory pathways, and to identify mediators that regulate bladder sensory hypersensitivity as a result of colitis. Our publications and preliminary data have shown that the brain-derived neurotrophic factor (BDNF)/TrkB system has a prominent role in the regulation of bladder activity. In this renewal application, we hypothesize that the phospholipase C-gamma (PLC?)-calcium (Ca2+) pathways are unique downstream of the increased endogenous BDNF/TrkB in bladder afferent neurons, and play an integral role in bladder afferent activation by Ca2+-dependent transcriptional and posttranslational regulation of neuroactive compounds during colitis. To address this hypothesis, three interrelated Specific Aims are proposed to examine the regulatory mechanism and the targets of the PLC?-Ca2+ pathways including Ca2+/calmodulin-dependent protein kinase (CaMK)II, cAMP-response element binding protein (CREB), calcitonin gene-related peptide (CGRP), and cerebellin 1 precursor (Cbln1) in bladder afferent neurons before and during colitis. In AIM 1, we will characterize the expression profiles of a series of components regulating Ca2+ mobilization (phospholipase C?, InsP3R-1, voltage-gated Ca2+ channels predominantly the N-type channel Cav2.2) and Ca2+-dependent neuronal activation (CaMKII and CREB) in bladder afferent neurons at 7 days and 21 days of colitis. This will be done at the molecular (mRNA and protein) and functional (intracellular Ca2+ recording and electrophysiology) levels. In AIM 2, we will examine the regulatory mechanism by which the PLC?-Ca2+ pathways are activated by endogenous BDNF in bladder afferent neurons during colitis. For this purpose, we will use a newly developed yet well-characterized BDNF+/- rat strain. In AIM 3, we will combine molecular biological, pharmacological, neurochemical, and behavioral tests to examine the functional role of the BDNF-Ca2+ axis in bladder hyperactivity during colitis. We will characterize how the Ca2+-dependent pathways are involved in CGRP and Cbln1 expression, and how they regulate bladder afferent neuronal hyperactivity and modulate bladder micturition parameters during colitis. For studies proposed above, we will utilize a variety of in vivo (transgenic animals, intrathecal delivery of drugs, behavioral studies and ex vivo/in vitro (DRG explants, isolated DRG neuron culture and transfection) systems. The localized colonic inflammation will be induced by intracolonic instillation of tri-nitrobenzene sulfonic acid (TNBS) in rat. As several small molecule antagonists of the Ca2+ pathways are under clinical trials in treatment of other pain symptoms, we anticipate that the current systematic studies will provide insights into forming therapeutic strategies in the treatment of visceral hypersensitivity.